Chloe Zhang
Plastic is a versatile material used for a variety of purposes, from food containers to packaging. However, one common issue with plastic is its tendency to absorb and retain odours. This phenomenon raises the question of whether hard plastic is permeable to smell. The answer lies in understanding the nature of odour molecules and the structure of plastic. Odour molecules are typically small and lightweight, allowing them to evaporate and float in the air, easily penetrating materials with microscopic pores or gaps. While plastic is considered inert, everyday plastics are not entirely inert and can release volatile components, such as plasticizers and additives, that contribute to their smell. Additionally, certain types of plastic, like non-rigid PVC, contain plasticizers that impart distinct odours. Thickness and material composition play a role in reducing the permeability of plastic to smells, as thicker plastic layers create more barriers for odour molecules to navigate. However, gases, including odorous molecules, generally have greater mobility than liquids, enabling them to permeate through plastic more effectively. Thus, hard plastic exhibits varying degrees of permeability to smell, influenced by factors such as thickness, material composition, and the nature of the odour molecules.
| Characteristics | Values |
|---|---|
| Permeability to smell | Plastic is quite permeable to smell compared to glass |
| Reason for permeability | Plastic has teeny-tiny pores that odour molecules can pass through |
| Plastic types with noticeable odours | Non-rigid PVC (polyvinyl chloride), acrylic, LDPE (low-density polyethylene) |
| Plastic additives with noticeable odours | Phthalates, bisphenol A, polyethylene oxide |
| Plastic properties | Plastic is inert, but some components are volatile at room temperature |
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What You'll Learn
- Plastic bags are non-permeable to most liquids but not to gases
- Plastic is porous to oxygen, which can spoil the contents
- Plastic isn't completely inert, it can exude volatile components
- Plasticizers like phthalates are added to make polymers flexible, and they have noticeable odours
- Plastic bags designed to store cannabis are thicker, with additional layers to prevent smells from escaping
Plastic bags are non-permeable to most liquids but not to gases
Plastic bags are designed to be non-permeable to liquids. However, gases can permeate through them. This is because gases, being more energized, bounce around more, and so have a higher chance of passing through the molecule-sized gaps in the plastic.
The molecules we smell are usually small and light, which is why they can float in the air. Plastic is quite permeable compared to other materials, such as glass. This is because there are tiny pores in plastic that odour molecules can pass through. For example, when you smell something through a plastic wrapper, the odour molecules are penetrating the plastic.
Plastic bags designed to store items with strong odours, such as weed, are made of thicker plastic with additional material around the edges. The zip lock on these bags is also double or triple-layered, which helps to keep all particles in the bag, not just solid or liquid ones.
Plastics in everyday use are usually made of artificial polymers derived from oil. Any smell comes from small molecules that are volatile at room temperatures, such as additives, leftover monomers, or breakdown products. For example, non-rigid PVC contains plasticizers such as phthalates, which have noticeable odours. Similarly, water in clear plastic bottles can acquire a distinct taste if left in the sun due to contamination by the products used to make the plastic, such as bisphenol A.
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Plastic is porous to oxygen, which can spoil the contents
Plastic is known to have a distinct smell, which is caused by the small molecules that are volatile at room temperatures. These molecules can be additives, leftover monomers from the polymerisation process, or breakdown products. This distinct smell can also be transferred to the contents of the plastic container, spoiling them.
Plastic is porous to oxygen, which can seep in through tiny pores and spoil the contents. This process is called mass transfer. The molecules we smell are usually small and light, allowing them to become airborne and float in the air. Plastics are quite permeable compared to other materials, such as glass.
The permeability of plastic to oxygen and other gases is due to the presence of tiny gaps or pores in the material. These pores allow gases and small molecules to pass through, while liquids, with their larger molecules, are unable to permeate as easily. This is why plastic bags are useful for storing items and preventing liquid leakage but are less effective at blocking smells.
To reduce the permeation of smells through plastic, some bags are designed with thicker material and additional layers, making it more difficult for the molecules to pass through. However, this does not completely block odours, and over time, the contents may still be affected by oxygen seepage, leading to spoilage.
Thus, it is important to consider the limitations of plastic when storing items, especially those that are sensitive to oxygen or susceptible to odour absorption. While plastic provides convenience and flexibility, its porosity to oxygen can be a factor in certain applications.
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Plastic isn't completely inert, it can exude volatile components
Plastic is considered chemically inert, but it can still give off a strong smell. This is because plastic isn't completely inert; it can exude volatile components. Common plastics can emit their more volatile components, such as plasticizers like bisphenols, which we can smell and taste. These plasticizers can also mimic oestrogen.
Plastics in everyday use are usually made of artificial polymers, which are derived from oil. The polymers consist of very long chains of atoms. In thermoplastics, these chains are not chemically bonded, whereas in thermoset plastics, the polymer strands are cross-linked. The smell does not come from these polymers but from small molecules that are volatile at room temperature. These could be additives, leftover monomers from the polymerisation process, or breakdown products.
Non-rigid PVC (polyvinyl chloride) contains plasticizers such as phthalates, which have noticeable odours. They are added to make a rigid polymer flexible. The water in clear drinks bottles made of PET (polyethylene terephthalate) that are left in the sun can become contaminated with some of the starting products used to make the plastic, such as bisphenol A, which could be the source of a taste in the water.
The smell of plastic is due to the tiny pores in the material that allow gases to move through more easily than liquids. This is because gas particles are more energised and can bounce around more, so any single particle has a higher chance of making it through the molecule-sized gaps in the plastic.
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Plasticizers like phthalates are added to make polymers flexible, and they have noticeable odours
Plasticizers are substances added to polymers and plastics to make them more flexible, reduce viscosity, and decrease friction during handling. They are especially important in the production of polyvinyl chloride (PVC), the third most widely used plastic. Without plasticizers, PVC is hard and brittle, but with them, it becomes flexible and suitable for various applications, such as vinyl siding, roofing, flooring, and plumbing.
Phthalates are a group of chemicals derived from phthalic acid and are commonly used as plasticizers in PVC. They enhance the processability of polymers and improve their flexibility, transparency, and durability. The most common phthalates include di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate (DBP), and diisononyl phthalate (DINP). Phthalates are compatible with PVC because they make it more pliable without significantly altering its other mechanical properties.
However, there are concerns about the safety of some phthalates, which have been linked to potential health and environmental risks. Low molecular weight ortho-phthalates, for example, have been classified as potential endocrine disruptors, and some developmental toxicity has been reported. Regulatory concerns have led to a move away from these classified substances, especially in Europe. As a result, non-phthalate plasticizers, such as adipate, citrate, and sebacate, are becoming more popular due to increased regulation and consumer demand for safer alternatives.
The unique smell of a new car is often attributed to plasticizers or their degradation products. While multiple studies on the makeup of this scent have not found significant amounts of phthalates, it is believed that the "new car smell" is due to their extremely low volatility and vapour pressure. Nevertheless, plasticizers like phthalates do have noticeable odours, and their presence can impact the overall aroma of a product.
In conclusion, plasticizers like phthalates play a crucial role in making polymers flexible and usable, but they also contribute to the odour profile of the final product. The distinctive smell of certain plastics and polymers can be partly attributed to the presence of these plasticizers, even if the specific compounds are not always easily detectable.
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Plastic bags designed to store cannabis are thicker, with additional layers to prevent smells from escaping
Plastic containers are commonly used to store food and other items. However, one of the drawbacks of using plastic containers is that they can absorb and retain odours, which can be challenging to remove. This occurs because the molecules responsible for odours are often small and light, allowing them to become airborne and penetrate through the tiny pores in plastic materials.
To address this issue, specialised plastic bags have been designed for storing cannabis, which is known for its strong odour. These bags are thicker and incorporate additional layers to prevent smells from escaping, ensuring discreet storage and transportation. The use of multiple layers creates a more airtight environment, reducing oxygen exposure and helping to maintain the freshness and potency of the cannabis.
Activated carbon linings are commonly used in these bags as they are highly porous and effective at neutralising odours. Other materials such as nylon, polyethylene terephthalate (PET), and polyethylene (PE) are also utilised for their odour-blocking properties. Some bags feature airtight zippers, lockable compartments, and built-in pouches for added protection against odour leaks.
It is recommended to combine the use of smell-proof bags with other practices for optimal cannabis storage. This includes frequent "burping" of the bags to release excess moisture and replenish oxygen, controlling humidity levels, storing in a cool and dark place, and proper labelling and dating. While plastic bags can serve as a temporary solution, alternative storage options like glass jars with airtight seals may provide better protection against moisture and oxygen.
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Frequently asked questions
Yes, hard plastic is permeable to smell. Odoriferous molecules are small and light, and plastics have tiny pores, so the molecules can penetrate through the plastic.
To get smells out of hard plastic, first scrub the container with soap and hot water. Then, you can try one of the following methods:
- Place used coffee grounds in the container and let it sit until the odour is gone.
- Crumple up newspaper, stuff it into the container, and leave it overnight.
- Place a piece of charcoal in the container and seal the lid until the odour is gone.
Plastics are made of artificial polymers that are derived from oil. The polymers consist of long chains of atoms that are not chemically bonded to each other. The smell comes from small molecules that are volatile at room temperature, such as additives or leftover monomers from the polymerisation process.
Yes, non-rigid PVC contains plasticisers such as phthalates, which have noticeable odours. Acrylic, a clear rigid plastic, has a sharp smell of methyl methacrylate.
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